I noticed something recently that really surprised me, and I wonder if it relates in some way to the discrepancies between different observers' reports of edge sharpness in a given binocular model. For the record, I am an eyeglasses wearer and a person who easily notices chromatic abberations in binoculars when I look for it, though it usually doesn't bother me otherwise. In comparing sharpness outside the very center of the field of view (I was trying to tease out the seperate effects of distortion and field curvature) and off-axis chromatic abberation in my beloved 8x32 Leica BA Utra/Trinovid and my new 8x32 Zeiss FL, I noticed that eye position can have a big effect on edge sharpness and off-axis CA in a way that I have never before noticed. For me, in normal use, the Zeiss has extremely little off-axis CA, while there is quite a bit in the Leica, but the Leica retains much better sharpness outside the center of the field. Generally, when thinking about eye position, one assumes that it is important to have one's eyes alligned and centered with the oculars and exit pupil, or else the view will be compromised--and this is generally true--but what I found, for example when looking at the edge of the field at the top of the view, was that if I shift my eye to look more through the bottom of the exit pupil (rather than being centered on it), that chromatic abberation is reduced in the Leica, and if I look through the top of the exit pupil, that edge sharpness improves considerably in the Zeiss. This is an uncomfortable manuever to perform, and is of no utility or significance when it comes to actually using these binoculars, but again, I wonder if it relates in some way to the different impressions different observers have of the same binos. Let me make it clear that I'm not suggesting that some observers are not properly alligning their eyes with the ocular and exit pupil, but that perhaps our eyes match up with it or sample it differently when we are using the same bino correctly.
--Alexis Powell
[QUOTE=Alexis Powell]I noticed something recently that really surprised me, and I wonder if it relates in some way to the discrepancies between different observers' reports of edge sharpness in a given binocular model. For the record, I am an eyeglasses wearer and a person who easily notices chromatic abberations in binoculars when I look for it, though it usually doesn't bother me otherwise. In comparing sharpness outside the very center of the field of view (I was trying to tease out the seperate effects of distortion and field curvature) and off-axis chromatic abberation in my beloved 8x32 Leica BA Utra/Trinovid and my new 8x32 Zeiss FL, I noticed that eye position can have a big effect on edge sharpness and off-axis CA in a way that I have never before noticed. For me, in normal use, the Zeiss has extremely little off-axis CA, while there is quite a bit in the Leica, but the Leica retains much better sharpness outside the center of the field. Generally, when thinking about eye position, one assumes that it is important to have one's eyes alligned and centered with the oculars and exit pupil, or else the view will be compromised--and this is generally true--but what I found, for example when looking at the edge of the field at the top of the view, was that if I shift my eye to look more through the bottom of the exit pupil (rather than being centered on it), that chromatic abberation is reduced in the Leica, and if I look through the top of the exit pupil, that edge sharpness improves considerably in the Zeiss. This is an uncomfortable manuever to perform, and is of no utility or significance when it comes to actually using these binoculars, but again, I wonder if it relates in some way to the different impressions different observers have of the same binos. Let me make it clear that I'm not suggesting that some observers are not properly alligning their eyes with the ocular and exit pupil, but that perhaps our eyes match up with it or sample it differently when we are using the same bino correctly.
--Alexis Powell[/QUOTE]
Alexis,
I can affirm your observations. I recently discovered that I could improve contrast in the normal Ultravid image by repositioning my eye in an unnatural manner...at the expense of increased CA, I might add.
I believe eyeglasses can seriously degrade the "normal" image delivered by any binocular. There are many reasons for this, but it should be obvious that eyeglasses increase the complexity of the optical system, often at the expense of image quality.
John